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Date: Thu, 25 Sep 2008 07:33:24 -0700
From: "Martin Bligh" <mbligh@mbligh.org>
To: "Peter Zijlstra" <peterz@infradead.org>
Subject: Re: [RFC PATCH 1/3] Unified trace buffer
Cc: "Martin Bligh" <mbligh@google.com>, "Steven Rostedt" <rostedt@goodmis.org>,
       "Linus Torvalds" <torvalds@linux-foundation.org>,
       linux-kernel@vger.kernel.org, "Ingo Molnar" <mingo@elte.hu>,
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       "David Wilder" <dwilder@us.ibm.com>, hch@lst.de,
       "Tom Zanussi" <zanussi@comcast.net>,
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> I rather like this idea, as it gives small entries (the common case) the
> least overhead but does allow for larger ones.
>
> By also putting the time in there you can do the merge sort iterator,
> Linus was right that everybody wants this anyway.
>
> As for delta encoding the time, we could make the tick log the absolute
> time packet, that's at least 100Hz and it already has to compute the
> full gtod thing anyway.
>
> I don't much like Linus' idea of bringing type information back into the
> primitive header (sorry Linus ;-)). I'd much rather keep that
> abstraction in the next layer.

There is part of the type stuff that belongs in the lower layer, it seems -
the padding events for the up-to-end-of-page buffering, and the timestamp
extensions. It seems wrong to split those across two layers.

But perhaps we can keep a couple of bits for this, and three of the bits
to represent the length of the data payload (maybe in 4 byte multiples
rather than bytes?) That'd let up to 28 bytes as a payload in a short event.